The objective of the proposed study is to obtain in vitro quantitative fluid dynamic characteristics of various prosthetic heart valves and hence, to evaluate the performance of each prosthetic valve. The specific variables to be measured include: velocity profiles, pressure drop, drag force and turbulent shear stresses around the prosthetic valves in both steady and pulsatile flows simulated in the mock-circulator system with transparent blood analog fluids. The Laser-Doppler Anemometry (LDA) will be used to obtain accurate fluid dynamic characteristics of prosthetic values such as separation, regurgitation and turbulent stress. These variables normally can not be measured with hot-film anemometry. Several prosthetic valves including caged-ball valve (Starr-Edwards), tilting disk valve (Bjork-Shiley), porcine xenograft (Carpentier-Edwards) and pericardial tissue valve (Ionescu-Shiley) will be used in this investigation. Steady and unsteady turbulent flows past the prosthetic valves will be analyzed theoretically with a turbulence model. The result will be verified from experimental measurements. The experimental study complemented by the theoretical analysis will concentrate on the quantification of the pulsatile fluid dynamics of flow past heart valve prosthesis. These will include turbulent stress distribution in the vicinity of the valve leaflets and in the aortic arch, pressure drop across the valve leaflets and identification of regions with low shear and relative stasis which will be conductive to thrombus formation. The optimum orientation of the non-symmetrical valve leaflets with respect to the sinuses will also be investigated.